Spectacles utilising electroactive lenses are typically used to provide the wearer with two or more selectable focus settings. Refer, for example, to Blum et al, “Optical Lens System with Electro-Active Lens Having Alterably Different Focal Lengths”, U.S. Pat. No. 6,619,799, the contents of which are herein incorporated by reference.
While they have myriad uses, electroactive spectacles are particularly useful as an improved replacement for the bifocal spectacles typically worn by presbyopes, since, unlike standard bifocals, they provide the wearer with near and far focus settings that span the full visual field of the spectacles.
Electroactive spectacles include three essential elements: a pair of electroactive lenses, a controller (or pair of controllers) for controlling the lenses, and a mechanism for the wearer to select a focus setting.
Current electroactive spectacles typically provide the user with two mechanisms for selecting focus. The first mechanism allows the user to manually select focus using a button or switch incorporated in the spectacles. The second mechanism automatically infers the user's desire for near focus when the spectacles are tilted forward relative to the horizontal plane, and a desire for far focus otherwise. Neither mechanism is ideal.
When a person with normal vision fixates on a near object their visual system is able to automatically focus on the object without conscious control. Fixation is the only control mechanism required, and thus suggests the ideal for a corresponding mechanism in electroactive spectacles. While it is desirable to implement such a mechanism entirely within the spectacles, as mentioned by Blum et al in aforementioned U.S. Pat. No. 6,619,799, the low weight and slim form-factor desired in modern spectacles makes this difficult.